Technical References - [url]
[url], [input], and [convertchars] assure proper formatting and interpretation of text
[url], [input], and [convertchars] are used to prevent certain characters from being misinterpreted. You use each of them in specific cases, which are easily confused.
Here are the problematic characters:
WebDNA: &, =, ^, ~, !,\, / [, ], and anything else used as code
URLs: Only alphanumeric values, - and _ are allowed
Platform differences: Unix, Windows and Mac all have their own upper ASCII mapping, such as curly quotes, em dashes, degree signs, etc.
URL converts characters to legal URL characters, such as a space to . When WebDNA works with [url]'d values, it automatically decodes them, so no worries about ending up with a bunch of percent signs everywhere.
Where to use: [search], [replace], [append], links, [showif], [hideif], [listwords], or any place you are working with values that the user inputs and you have no control over, or variables from databases where the value may contain problematic characters (e.g., item descriptions). If you are using guaranteed clean values, such as dates, Y/N values, numbers, or SKUs, you have nothing to worry about.
It is common in form submission validation to ask if a value is blank by using [showif [value]=] However, if [value] would contain an !, the exclamation point would be interpreted to mean "does not equal", and therefore the expression would be true, exactly the opposite of what was intended. [showif [url][value][/url]=] prevents this.
([date] is not URL'd because we know it will be clean.)
[showif [url][subjectline][/url]=]Error! You must enter a subject line[/showif]